Nitrogen-containing materials, or nitrides, are widely used in the fabrication of integrated circuits. For example, nitrides are used as transistor gate dielectrics, insulators between metal levels, barriers to prevent oxidation and other diffusion, hard masks, passivation layers, spacer materials in transistors, anti-reflective coating materials, layers in non-volatile memories, etc.
To take one example, nitrogen-containing dielectric layers, e.g., silicon dioxide having incorporated nitrogen, are used to form gate dielectrics in many metal-oxide-semiconductor (MOS) transistors. The gate dielectric layer separates a “metal” layer from a semiconductor layer. Typically, the “metal” layer functions as a gate electrode and is formed of silicon, rather than a metal. The silicon is typically doped, e.g., with boron, for increased conductivity. The gate electrode functions to regulate the flow of electrons across the semiconductor layer.
During operation of the transistor, the gate dielectric prevents undesirable electron flow between the semiconductor layer and the gate electrode. The dielectric layer also helps to maintain the long term reliability of the transistor by maintaining the electrical properties of the transistor. For example, the dielectric layer typically prevents dopant diffusion between the gate electrode and the semiconductor layer and typically also resists electrons from being injected into it. Among other things, it will be appreciated that dopant diffusion and/or electron injection can degrade the electrical properties of the transistor by, among other things, altering the threshold voltage needed to control electron flow through the semiconductor layer and by altering the charge-carrying behavior of various layers.
Nitridation of the dielectric layers can improve the thermal and electrical stability of the dielectric layers. Many nitrogen-containing gate dielectric layers, such as high k dielectrics and silicon oxide layers that contain nitrogen, can offer a higher dielectric constant and can offer increased resistance to electron injection. In the addition, nitrogen-containing gate dielectric layers can offer increased resistance to dopant diffusion, relative to similar dielectric layers without nitrogen. Conventional methods of incorporating nitrogen into gate dielectrics can be difficult to control, however, particularly where the gate dielectrics are very thin. Moreover, the amount of incorporated nitrogen may be less than desired in some applications.
Consequently, there is a need for improved methods for incorporating nitrogen to forming nitrogen-containing materials.